Internal combustion engines have a cylinder block and at least one cylinder head which are connected to one another at their assembly end sides so as to form at least one cylinder, that is to say a combustion chamber.
To hold the pistons or the cylinder liners, the cylinder block has a corresponding number of cylinder bores. The pistons are guided in the cylinder liners in an axially movable fashion and form, together with the cylinder liners and the cylinder head, the combustion chambers of the internal combustion engine.
The cylinder head conventionally serves to hold the valve drive. To control the charge exchange, an internal combustion engine requires control elements and actuating devices for actuating the control elements. During the charge exchange, the combustion gases are discharged via the outlet openings and the combustion chamber is charged, that is to say the fresh mixture or the charge air is inducted, via the inlet openings. To control the charge exchange, in four-stroke engines, use is made almost exclusively of lifting valves as control elements, which lifting valves perform an oscillating lifting movement during the operation of the internal combustion engine and which lifting valves open and close the inlet and outlet openings in this way. The valve actuating mechanism required for the movement of the valves, including the valves themselves, is referred to as the valve drive.
According to the prior art, the inlet ducts which lead to the inlet openings, and the outlet ducts, that is to say the exhaust lines which adjoin the outlet openings, are at least partially integrated in the cylinder head. The exhaust lines of the outlet openings of a single cylinder are in this case generally merged—within the cylinder head—to form a component exhaust line associated with the cylinder, before said component exhaust lines are merged—commonly to form a single overall exhaust line. The merging of exhaust lines to form an overall exhaust line is referred to generally, and within the context of the present invention, as an exhaust manifold.
Downstream of the at least one manifold, the exhaust gases may then supplied to a turbine, for example the turbine of an exhaust-gas turbocharger, and may be conducted through one or more exhaust-gas aftertreatment systems as appropriate.
The production costs for the turbine may be comparatively high because the—often nickel-containing—material used for the thermally highly loaded turbine housing is expensive, in particular in relation to the material preferably used for the cylinder head, for example aluminum. Not only the material costs themselves, but also the costs for the machining of said materials used for the turbine housing are relatively high.
From that which has been stated above, it follows that, with regard to costs, it would be highly advantageous if a turbine could be provided which could be produced from a less expensive material, for example aluminum or cast iron.
The use of aluminum would also be advantageous with regard to the weight of the turbine. This is true in particular when it is taken into consideration that an arrangement of the turbine close to the engine leads to a relatively large-dimensioned, voluminous housing. This is because the connection of the turbine and cylinder head by means of a flange and screws requires a large turbine inlet region on account of the restricted spatial conditions, also because adequate space must be provided for the assembly tools. The voluminous housing is associated with a correspondingly high weight. The weight advantage of aluminum over a highly loadable material is particularly pronounced in the case of a turbine arranged close to the engine on account of the comparatively high material usage.
To be able to use cheaper materials for producing the turbine, the turbine according to the prior art is provided with a cooling arrangement, for example with a liquid-type cooling arrangement, which significantly reduces the thermal loading of the turbine and of the turbine housing by the hot exhaust gases and therefore permits the use of thermally less highly loadable materials.
In general, the turbine housing is provided with a coolant jacket in order to form a cooling arrangement. The prior art discloses both concepts in which the housing is a cast part and the coolant jacket is formed, during the casting process, as an integral constituent part of a monolithic housing, and concepts in which the housing is of modular construction, wherein during assembly a cavity is formed which serves as a coolant jacket.
A turbine designed according to the latter concept is described for example in the German laid-open specification DE 10 2008 011 257 A1. A liquid-type cooling arrangement of the turbine is formed by virtue of the actual turbine housing being provided with a casing, such that a cavity into which coolant can be introduced is formed between the housing and the at least one casing element arranged spaced apart therefrom. The housing which is expanded to include the casing arrangement then encompasses the coolant jacket. EP 1 384 857 A2 likewise discloses a turbine whose housing is equipped with a coolant jacket. DE 10 2007 017 973 A1 describes a construction kit for forming a vapor-cooled turbine casing.
On account of the high specific heat capacity of a liquid, in particular of water which is conventionally used, large amounts of heat can be extracted from the housing by means of liquid-type cooling. The heat is dissipated to the coolant in the interior of the housing and is discharged with the coolant. The heat which is dissipated to the coolant is extracted from the coolant again in a heat exchanger.
It is basically possible for the liquid-type cooling arrangement of the turbine to be equipped with a separate heat exchanger or else—in the case of a liquid-cooled internal combustion engine—for the heat exchanger of the engine cooling arrangement, that is to say the heat exchanger of a different liquid-type cooling arrangement, to be used for this purpose. The latter merely requires corresponding connections between the two circuits.
It must however be taken into consideration in this context that the amount of heat to be absorbed by the coolant in the turbine may amount to 40 kW or more if materials that can be subjected to only low thermal loading, such as aluminum, are used to produce the housing. It has proven to be problematic for such a large amount of heat to be extracted from the coolant, and discharged to the environment by means of an air flow, in the heat exchanger.
Modern motor vehicle drives are duly equipped with high-powered fan motors in order to provide, at the heat exchangers, the air mass flow required for an adequately high heat transfer. However, a further parameter which is significant for the heat transfer, specifically the surface area provided for the heat transfer, cannot be made arbitrarily large or enlarged arbitrarily because the space availability in the front-end region of the vehicle, where the various heat exchangers are generally arranged, is limited.
Aside from the heat exchanger for engine cooling, modern motor vehicles often have further heat exchangers, in particular cooling devices.
A charge-air cooler is often arranged on the intake side of a supercharged internal combustion engine in order to contribute to improved charging of the cylinders. The heat dissipation via the oil sump by heat conduction and natural convection is often no longer sufficient to adhere to a maximum admissible oil temperature, such that in individual situations an oil cooler is provided. Furthermore, modern internal combustion engines are increasingly being equipped with exhaust-gas recirculation (EGR). Exhaust-gas recirculation is a measure for counteracting the formation of nitrogen oxides. To obtain a considerable reduction in nitrogen oxide emissions, high exhaust-gas recirculation rates are required, which demand cooling of the exhaust gas to be recirculated, that is to say a compression of the exhaust gas by cooling. Further coolers may be provided, for example in order to cool the transmission oil in the case of automatic transmissions and/or to cool hydraulic fluids, in particular hydraulic oil, which is used within hydraulically actuable adjusting devices and/or for steering assistance. The air-conditioning condenser of an air-conditioning system is likewise a heat exchanger which must dissipate heat to the environment during operation, that is to say which requires an adequately large air flow and must therefore be arranged in the front-end region.
On account of the extremely limited spatial conditions in the front-end region and the multiplicity of heat exchangers, the individual heat exchangers may not be able to be dimensioned as required.
In fact, it may not be possible in the front-end region to arrange an adequately large heat exchanger for liquid-type cooling of the turbine in order to be able to also dissipate the large amounts of heat that arise when using materials that can be subjected to only low thermal loading.
In the structural design of a cooled turbine, a compromise between cooling capacity and material is therefore necessary.
To be able to use cheaper materials for the turbine, it is also possible according to the prior art for the turbine to be equipped, on the exhaust-gas side, with insulation. Such a concept is disclosed in the international application WO 2010/039590 A1.